Highly twisted bipolar emitter for efficient nondoped deep-blue electroluminescence

Three novel bipolar deep-blue emitters, 1-(4-(tert-butyl)pheny1)-2-(4-(9,9-diphenylacridin-10(9H)-yl) phenyl)-1H-phenanthro[9,10-d]imidazole (DPACTPI), 1-(4-(tert-butyl)pheny1)-2-(4'-(9,9-diphenylacridin-10(9H)-yl)-[11'-biphenyl]-4-yl)-1H-phenanthro[9,10-d]imidazole (DPACPhTPI) and 2(4-(9,9-diphenylacridin-10(9H)-yl)pheny1)-1-(4-(trifluoromethyl)pheny1)-1H-phenanthro[9,10-d]imid-azole (DPACFPPI), employing the donor 9,9-diphenyl-9,10-dihydroacridine (DPAC) and the acceptor, phenanthroimidazole, were designed and synthesized. The highly twisted conformations between DAPC and phenanthroimidazole in the molecules efficiently interrupt molecular it pi-conjugation and inhibit pi-pi intermolecular interactions, resulting in good thermal stability and efficient deep-blue emission. The three phenanthroimidazole derivatives in non-doped OLEDs exhibited deep-blue emission. In particular, DPACPhTPI-based nondoped device showed an excellent performance with maximum external quantum efficiency (EQE) of 3.50%, maximum current efficiency (CE) of 1.38 cd/A, maximum power efficiency (PE) of 1.40 lm/W and CIE coordinate of (0.156, 0.047), which is among the best results for OLEDs with a similar color. The high radiative exciton utilization could be resulted from hybridized local and charge transfer (HLCT).(C) 2017 Elsevier Ltd. All rights reserved.